The present invention relates to a hoist used in a container crane.
FIG. 1 shows a container crane and FIG. 2 illustrates a boom derrick, a head block lifter and a trolley traverser used in the container crane. More specifically, the container crane comprises land- and seaward rails Q1 and Q2 on a quay P at harbor S, a traveler 2 with legs 1a and 1b running on the rails Q1 and Q2, a girder 3 substantially horizontally mounted on a top of the traveler 2, a boom 4 pivoted to a tip of the girder 3 so as to be swung upward, a main trolley 5 traversing along the girder 3 and boom 4, a head block 6 suspended from and vertically movable relative to the trolley 5, a spreader 7 mounted on the block 6 and with which a container C is to be locked, a first catenary trolley 19 positioned closer to a base end of the girder 3 than the main trolley 5 and traversing along the girder 3 and boom 4 and a second catenary trolley 20 positioned closer to the tip of the boom 4 than the main trolley 5 and traversing along the girder 3 and boom 4.
In the container crane as described above, unloading of the container C from a ship V to the quay P and loading of the same from the quay P to the ship V are carried out in combination of operations such as motion of the traveler 2 along the quay P, traverse of the trolley 5 on the girder 3 and boom 4, vertical motion of the block 6 relative to the trolley 5 and locking of the container C by the spreader 7.
Disposed on the girder 3 is a machine room 8 with a drum 11 for derricking motion of the boom 4, drums 15a and 15b for vertical motion of the block 6, a drum 13 for traverse of the main trolley 5 and drums 9a and 9b for traverse of the catenary trolleys 19 and 20.
Rotation of the drum 11 in normal and reverse directions causes a boom-derricking rope 12 to be wound and unwound, respectively, resulting in change of angle of the boom 4 to the girder 3.
Rotation of the drums 15a and 15b in normal and reverse directions causes block-lifting ropes 16a and 16b to be wound and unwound, respectively, resulting in vertical motion of the block 6 relative to the trolley 5.
Rotation of the drum 13 in normal and reverse directions causes trolley-traversing ropes 14a and 14b to be wound and unwound, resulting in traverse of the trolley 5 towards the base and tip ends of the boom 4, respectively, since the rope 14a is locked at its opposite ends to the drum 13 and engaged at its intermediate portion with the trolley 5 via the base end of the girder 3 and the rope 14b is locked at its opposite ends to the drum 13 and engaged at its intermediate portion with the trolley 5 via the tip of the boom 4.
Rotation of the drums 9a and 9b in normal.and reverse directions causes trolley-traversing ropes 10a and 10b to be wound and unwound, resulting in traverse of the trolleys 19 and 20 towards the base and tip ends of the boom 4, respectively, since the rope 10a is locked at its opposite ends to the drums 9a and 9b and engaged at its intermediate portion with the trolley 19 via the base end of the girder 3 and the rope 10b is locked at its opposite ends to the drums 9a and 9b and engaged at its intermediate portion with the trolley 20 via the tip of the boom 4 and since the trolleys 19 and 20 are interconnected through a rope 17.
The catenary-trolley drums 9a and 9b are adapted to be rotated in synchronization with rotation of the main-trolley drum 13. The first catenary trolley 19 follows after the main trolley 5 so as to be positioned intermediately between the base end of the girder 3 and the trolley 5. The second catenary trolley 20 follows after the main trolley 5 so as to be positioned intermediately between the tip end of the boom 4 and the trolley 5.
The catenary trolleys 19 and 20 have rollers (not shown) pivoted to the trolleys 19 and 20 to support the main-trolley-traversing ropes 14a and 14b from below, respectively. The roller pivoted to the trolley 19 serves to suppress any excessive loosening of the rope 14a between the base end of the girder 3 and the trolley 5. The roller pivoted to the trolley 20 serves to suppress any excessive loosening of the rope 14b between the tip of the boom 4 and the trolley 5.
In recent years, there is a trend of increased traverse distance of the main trolley 5 as well as increased lift of the head block 6 in such container crane in association with a tendency of building larger-sized ships V.
In the conventional container crane, however, the block-lifting ropes 16a and 16b are wound on sheaves 18 pivotally supported at four corners of the block 6 to have eight turns in total so as to suspend the block 6 from the trolley 5. Therefore, increased traverse distance of the main trolley 5 and/or increased lift of the head block 6 will lead to prolongation of the block-lifting ropes 16a and 16b and increase in size of the block-lifting drums 15a and 15b. This may disadvantageously result in increase in weight of the system above the traveler 2 and/or difficulties in maintenance and inspection of the ropes 16a and 16b. 
The present invention was made to solve the above problems and has its major object to provide a hoist which is light in weight and compact in size.
According to a hoist of the invention drums with independent drive sources are mounted on a trolley and an unwound end of the head-block-lifting rope wound around each of the drums is locked on a suspension piece of a container, which suppress any need of the ropes in longer length and the drums in larger size.
According to a hoist of the invention sun gears, carriers and planetary gears in each of the drums as well as internal teeth in each of the drums for integral rotation with the drum provide a speed reducing mechanism for transmitting rotation of the drive source to the drum, which contributes to make the entire hoist compact in size.
According to a hoist of the invention provided between two drums is a differential gear mechanism for transmitting rotation of drums to an output shaft. Rotation of a drive shaft of the differential gear mechanism may be suppressed to synchronize rotation of the two drums.
According to a hoist of the invention provided between two drums is a differential gear mechanism for transmitting rotation of the two drums to an output shaft. The drive shaft of the differential gear mechanism is rotated to vary rotation of the two drums relatively to each other.
According to a hoist of the invention when the trolley is to be accelerated, a link is displaced in position in a predetermined direction by an actuator. The positional displacement of the link is transmitted to two paired drums via torque arms so that the drums positioned,ahead in the moving direction of the trolley are rotated in rope-winding direction and the drums positioned behind in the moving direction of the trolley are rotated in rope-unwinding direction. As a result, tensions on the ropes at positions ahead and behind in the moving direction of the trolley are adjusted to apply a force directed in the moving direction of the trolley on the suspension piece.
When the trolley is to be decelerated, the link is displaced in position in a direction opposite to the direction during the acceleration. The positional displacement of the link is transmitted to the two paired drums via the torque arms. The drums positioned ahead in the moving direction of the trolley are rotated in rope-unwinding direction and the drums positioned behind in the moving direction of the trolley are rotated in rope-winding direction. As a result, tensions on the ropes positioned ahead and behind in the moving direction of the trolley are adjusted to apply a force directed in a direction opposite to the moving direction of the trolley on the suspension piece of the container.